Bug report #1574

Displaying ECW raster images is very slow

Added by luca76 - about 15 years ago. Updated over 14 years ago.

Assignee:Frank Warmerdam -
Affected QGIS version: Regression?:No
Operating System:Windows Easy fix?:No
Pull Request or Patch supplied: Resolution:worksforme
Crashes QGIS or corrupts data: Copied to github as #:11634



I have QGIS 1.0.1 for windows installed from OSGEO4W.

If I try to open a simple ECW (67 MB), QGIS is taking too long to open it (about 30-40 seconds). It seems that it doesn't use overviews anymore.

Warmerdam says from OSGEO4W mailing list:

The ECW driver does not report having any specific overview levels
and this defeats certain optimizations in the statistics computation.
I believe this has a bad effect when an ecw layer is first added to
qgis but browsing after that should be fast.

The fix is to make the histogram computing logic smarter
(I'm not positive if QGIS is using it's own or GDAL's logic)
so that for formats like ECW with "arbitrary overviews" a
small overview sample of data will be fetched for statistics.

I believe this issue is the same in all modern QGIS+GDAL
builds, not just specifically in OSGeo4W or windows.


#1 Updated by Giovanni Manghi almost 15 years ago

I this still true?

On qgis 1.2 from trunk it took under a second to open a 56.5mb ECW raster image. The same under windows with qgis 1.0.2.

Please leave feedback.

#2 Updated by Giovanni Manghi almost 15 years ago

  • Resolution set to worksforme
  • Status changed from Open to Closed

Tested again on different platforms and boxes, and seems fine, at least with the data in ecw format I have. I close this, but please reopen if necessary.

#3 Updated by luca76 - over 14 years ago

confirmed, 1.3.0: now it's MUCH faster!

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